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Transformer Wire Current Capacity

J

Jim Thompson

Jan 1, 1970
0
Why yes, I do sometimes. But even at the frequencies used by modern
switchers the skin depth becomes an issue. At 1MHz in copper, it's
about 2.6 mils. For a winding that needs to handle several amps (and
therefore need to use wire with an effective diameter considerably more
than 5 mils), it's worth thinking about. It's not unusual to see Litz
wire being used in such transformers.

Cheers,
Tom

Litz is important even at 20KHz.

After melting a few bobbins I did some calculations and discovered the
source of the heat... the 9th harmonic matters :-(

...Jim Thompson
 
R

Roy L. Fuchs

Jan 1, 1970
0
Why yes, I do sometimes. But even at the frequencies used by modern
switchers the skin depth becomes an issue. At 1MHz in copper, it's
about 2.6 mils. For a winding that needs to handle several amps (and
therefore need to use wire with an effective diameter considerably more
than 5 mils), it's worth thinking about. It's not unusual to see Litz
wire being used in such transformers.

I wound transformers in an engineering lab for 8 years, I know when
to use Litz.

I am talking about the frequency in question here, not switcher
basics seminars.
 
T

Terry Given

Jan 1, 1970
0
Tom said:
Why yes, I do sometimes. But even at the frequencies used by modern
switchers the skin depth becomes an issue. At 1MHz in copper, it's
about 2.6 mils. For a winding that needs to handle several amps (and
therefore need to use wire with an effective diameter considerably more
than 5 mils), it's worth thinking about. It's not unusual to see Litz
wire being used in such transformers.

Cheers,
Tom

and it pops up at 50/60Hz, too, where skin depth in Cu is around 9mm. It
usually wont make an appearance until you get to mains distribution size
(LOTS of Cu, many layers), but I've seen it myself in a small 600A
coupled 3-phase choke.

M.P. Perry's book, Low Frequency Electromagnetic Design, is a must-read.
See fig. 2-11b - "1,600A carrier current line trap in 230kV substation",
concentrically wound with varying-thickness conductor, specifically
because of skin/proximity effect.

Ever heard of "Roebel" transposed cable? fig. 3-5b - rectangular strands
which are transposed every 10cm or so. Often used in BIG transformers
and generators......

Cheers
Terry
 
L

legg

Jan 1, 1970
0
I was musing about my MOT, with 143 turns of either skinny #18 or fat #19
http://www.abiengr.com/~sysop/images/MOT-primary2.jpg
- it's probably some metric size - anyway, I go googling for "wire table"
and this is one of the hits:
http://www.thelearningpit.com/elec/tools/tables/Wire_table.htm . And I get
to #18, and it says, "Max Amps: 0.5390".

?????!?!?!?!??!!!!!! This MOT draws about 2.5 amps while IDLING! I read
somewhere in some electronics hobbyist mag decades ago, in an article
about transformer rewinding, that #22 was good for an amp in a
transformer. Proportionally (proportionately?), #18 should be good for
FIVE AMPS! So, I'm wondering where the guy got his figures, but I got so
het up I haven't even checked any of the other google hits, so I'll
probably be enlightened in no uncertain terms. ;-) Anyway, my interest
was I've got a potload of #24 wire from scrounged telephone trunk scraps,
and was wondering how many #24's I'd have to put in parallel to equal a
#18. ... Hmmm, according to the calculator, if I use these ludicrously low
numbers from the chart, 4. I'll have to see if I have that kind of
ambition[1] tomorrow or so. ;-)

Cheers!
Rich
[1] and patience! ;-)

It's only out by an order of magnitude. In some fields, that's pretty
good.

It's interesting to see that lighter guages are not rated to carry any
current. I wonder what they are good for?

I don't mind spelling mistakes, just so long as they're consistent.

RL
 
J

John Fields

Jan 1, 1970
0
I was musing about my MOT, with 143 turns of either skinny #18 or fat #19
http://www.abiengr.com/~sysop/images/MOT-primary2.jpg
- it's probably some metric size - anyway, I go googling for "wire table"
and this is one of the hits:
http://www.thelearningpit.com/elec/tools/tables/Wire_table.htm . And I get
to #18, and it says, "Max Amps: 0.5390".

?????!?!?!?!??!!!!!! This MOT draws about 2.5 amps while IDLING! I read
somewhere in some electronics hobbyist mag decades ago, in an article
about transformer rewinding, that #22 was good for an amp in a
transformer. Proportionally (proportionately?), #18 should be good for
FIVE AMPS! So, I'm wondering where the guy got his figures, but I got so
het up I haven't even checked any of the other google hits, so I'll
probably be enlightened in no uncertain terms. ;-) Anyway, my interest
was I've got a potload of #24 wire from scrounged telephone trunk scraps,
and was wondering how many #24's I'd have to put in parallel to equal a
#18. ... Hmmm, according to the calculator, if I use these ludicrously low
numbers from the chart, 4. I'll have to see if I have that kind of
ambition[1] tomorrow or so. ;-)

Cheers!
Rich
[1] and patience! ;-)

It's only out by an order of magnitude. In some fields, that's pretty
good.

---
So, by an order of magnitude you mean what? That he'd have to
parallel 40 #24's to equal a #18?
---
It's interesting to see that lighter guages are not rated to carry any
current. I wonder what they are good for?

---
Let me put on my Phil Allison hat here, you stupid fucking
cocksucker, just to let you know that that the lighter gauges are
used when smaller currents are desired. They're not rated to carry
_any_ current?

You need to be posting to alt.fucking.idiots.
I don't mind spelling mistakes, just so long as they're consistent.

---
Who gives a shit about what you mind? With or without your
acceptance, it's "gauge", no matter how many times you've seen it
spelled wrong or spelled it wrong yourself, and whether or not you
mind it being spelled incorrectly consistently.

Grrrr....
 
I

Ignoramus6482

Jan 1, 1970
0
Ratings for power transmission conductors are grossly underrated. The
reason for it is not only fire safety, but also the fact that lighter
gauge means more voltage drop, which means cost to consumer.

Without conservatve code requirements, builders would skimp on wire,
causing more expense to the consumer in the long run. The code
protects electricity consumers by demanding heavier gauge wire that
could be gotten away with.

This does not apply to microwaves.

i
 
R

Rich Grise

Jan 1, 1970
0
[ @%#!*&! ]
,,, With or without your
acceptance, it's "gauge", no matter how many times you've seen it
spelled wrong or spelled it wrong yourself, and whether or not you
mind it being spelled incorrectly consistently.

Grrrr....

There, there, John, we all know "gage" is a noun. :)

Cheers!
Rich
 
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